The present invention relates to a method of purifying aqueous effluents containing in particular peroxidized compounds.
It relates more particularly to a method of purifying aqueous effluents comprising a method for the anaerobic biological decomposition of the compounds contained in the effluent.
The effluents which can be treated by the method of the invention in particular those produced by methods of oxidizing organic compounds.
Among these methods, the method of oxidizing hydrocarbons such as cyclohexane is exploited on a large scale. Thus, the conversion of cyclohexane to cyclohexanol/cyclohexanone is used for the manufacture of adipic acid, a major chemical intermediate for the manufacture of many products such as in particular polyamides, polyesters, polyurethanes. This manufacture of cyclohexanol/cyclohexanone is carried out in large industrial units which produce annually up to a few hundreds of thousands of tones which generate large volumes of effluents. The constraints imposed for the protection of the environment require these effluents to be treated, in particular in order to reduce the chemical oxygen demand (COD).
The reduction of the COD of aqueous effluents has been performed for a very long time, by many methods including biological methods of treatment using enzymes.
These biological treatments can be classified mainly into three categories, namely the methods of aerobic and anoxic purification and the methods of anaerobic purification.
However, it is known that the methods of anaerobic purification of waste water, in particular that containing more than 1 g/l of degradable COD, are preferred to the methods of aerobic purification. Indeed, the anaerobic methods produce products which are useful and whose value can be enhanced, such as methane. Furthermore, the energy required for carrying out an anaerobic method is less than that used in an aerobic method. In addition, the methods of anaerobic purification produce a quantity of sludge which is substantially less than the aerobic methods.
However, methods of anaerobic purification cannot be used to treat aqueous effluents because the enzymes used are sensitive and can be destroyed by numerous compounds.
The Applicant has thus observed that the treatment of aqueous effluents produced by the method of converting cyclohexane in the synthesis of the cyclohexanol/cyclohexanone mixture by an anaerobic method can lead to a destruction of the enzymes. The use of such a method therefore appeared to be impossible.
One of the aims of the present invention is to provide a method of treating the effluents resulting from the manufacture of a cyclohexanol/cyclohexanone mixture and more particularly methods of oxidizing olefins to alcohols and/or acetones by an anaerobic biological purification method.
Indeed, the Applicant has observed that these effluents contain various organic compounds and peroxidized compounds. It has also observed that these peroxidized compounds have a toxic effect on the enzymes or bacteria used in the methods of biological purification.
To this effect, the invention provides a method of anaerobic biological purification of aqueous effluent containing peroxidized compounds and organic compounds which are biodegradable. This method is characteriz d in that it consists in.
treating the effluents in order to convert the peroxidized compounds to oxidized compounds,
purifying the deperoxidized aqueous effluents in a method of anaerobic biological treatment by decomposition to methane and carbon dioxide.
The Applicant has found that the aqueous effluents, after elimination by conversion of the peroxidized compounds, can be effectively purified and without damaging the enzymes and the bacteria in a conventional method of anaerobic biological treatment, with production of methane and carbon dioxide.
A general description of these anaerobic biological treatments is, for example, given in a communication presented by P.L. McCarty at the Second International Conference on Anaerobic Digestion on Jul. 9, 1981 in Travemundexe2x80x94Germany under the title xe2x80x9c100 years of anaerobic treatmentxe2x80x9d.
For the treatment of effluents containing mainly soluble organic compounds, a method of bioconversion has been developed under the name xe2x80x9cUpflow Anaerobic Sludge Blanketxe2x80x9d (UASB).
Such a method is described in many publications. There may be mentioned for example,
xe2x80x9cUpflow Sludge Blanket Processesxe2x80x9d, 3rd International Symposium on Anaerobic Digestion, 1983, Cambridge, by G. Lettinga et al.
xe2x80x9cAnaerobic of Raw Domestic Sewagexe2x80x9d by G. Lettinga et al. in Biotechnology and Bioengineering Vol. XXV, pp. 1701-1723,1983.